The discovery of RNA sequences of potential biomedical importance has dramatically outpaced chemists' ability to design and synthesize novel selective RNA-binding compounds. This is due largely to a gap in knowledge in the field with regard to fundamental determinants of selectivity. This proposal seeks to test the hypothesis that the sequence selectivity of an RNA-binding compound is directly related to its kinetic off rate or residence time in the desired binding site. While a generally accepted principle in the realm of protein and enzyme recognition, and tested also in the context of DNA recognition, to our knowledge this concept has not been applied to compounds binding RNA. This hypothesis will be tested via three Aims. First, well-validated (but low- throughput) techniques will be used to analyze the binding properties of a series of known RNA-targeted compounds. Second, a new analytical methodology developed in our laboratory termed Arrayed Imaging Reflectometry will be tested in the context of multiplex (high-throughput) assessment of RNA-binding kinetic constants. This will also involve the development of new statistical methods for the analysis of time-dependent array data. Third, we will examine the effect of systematic functional group modification on the binding kinetics and sequence selectivity of a novel compound discovered in our lab that targets a viral RNA critical to the HIV life cycle. Completion of the proposed research will provide a new paradigm for RNA-targeted molecular design based on consideration of binding kinetics, as well as a new analytical tool for high-throughput characterization of RNA binding, and new lead compounds targeting HIV.